This paper presents the latest results of a multi-year study at the University of Maryland, which has been focused on a modular, extensible, sustainable exploration architecture which emphasizes flight operations and minimizes the development of new systems. This paper synthesizes and extends the results of the past four years, focusing on a detailed system architecture and program plan for a series of human lunar landings. The paper lays out the preliminary design of the vehicles, including a human spacecraft comparable in size and configuration to the SpaceX Dragon; this vehicle is used for the crew cabin from launch throughout the entire mission, including lunar landing and ascent, to Earth entry, descent, and landing. The analysis shows that, while this approach gives up some lunar landed payload mass, it is both cost-optimal and higher in reliability, as no rendezvous maneuvers are required after lunar ascent to enable trans-Earth insertion.
The paper lays out, on a year-by-year basis, the launch model for a vibrant program which includes an evolutionary series of system flight tests, leading up to human lunar orbit in 2021 and first human landing in 2023. The hard requirement for this study was to produce a system which allows human lunar return in less than a decade from a present-day start, with an unbreakable budget cap of $3B/year, and which conducts at least one human mission to the moon each year to a variety of scientifically and visually interesting locations with increasing capabilities and complexities. This program is laid out in the paper, taking advantage of the modular nature of the transportation architecture to allow autonomous cargo missions to precede later human missions to the moon. While the human landing mission is always self-sufficient in terms of safe landing and reliable return to Earth, single- and multiple-launch cargo missions predeploy exploration assets such as unpressurized or small pressurized rovers, advanced science instruments, and logistics to permit extended surface stays. The cargo precursor missions will also provide surveys of the landing site to identify hazardous regions for the crew vehicle to avoid, and will serve as a navigation beacon to support pinpoint landings close to the cargo vehicle. The early demonstration of this capability will be critical, as a significant step will be taken when the cargo vehicle has sufficient power generation, energy storage, and auxiliary habitat volume to allow the crew to stay and continue to explore throughout the lunar night.
The reference program developed supports 12 human missions over the years from 2019-2030, including six lunar surface missions with up to 12T of pre-emplaced cargo supporting surface stays throughout a lunar night. The program also supports four exploration missions to locations in cislunar space, such as EarthMoon libration points and a lunar distant retrograde orbit. Throughout more than a decade of actively flying one or two human exploration missions per year, along with an evolutionary development flight test program and cargo missions in support, the program rigidly adheres to the $3B/year annual spending cap, and builds experience and technologies applicable to eventual human Mars exploration.